Conventionally, there has been known a substrate processing apparatus that controls a plasma density distribution by generating a magnetic field in a processing space where an electric field is present. In this substrate processing apparatus, electrons make a drift motion with a Lorentz force caused by the electric field and the magnetic field in the processing space into which a processing gas is introduced to be collided with molecules or atoms of the processing gas, so that plasma is generated.
By way of example, a conventional magnetron plasma processing apparatus includes a dipole ring magnet formed of multiple columnar anisotropic segment magnets arranged in a ring shape at an outside of a chamber, and as shown in FIG. 11, a uniform horizontal magnetic field B as a whole is formed by slightly deviating a direction of magnetization caused by the multiple columnar anisotropic segment magnets (see, for example, Patent Document 1). Further, FIG. 11 is a diagram (plane view) of the conventional magnetron plasma processing apparatus as viewed from above, and shows that a base end side of the direction of the magnetic field is indicated by N, a leading end side thereof is indicated by S, and positions rotated by 90° from N and S are respectively indicated by E and W.
However, the horizontal magnetic field B formed by the dipole ring magnet is directed only in one direction from N to S in the diagram. Further, in this magnetron plasma processing apparatus, the electric field is formed downward, so that the electrons travel from E to W by the drift motion by a Lorentz force. Consequently, plasma density is low on the E side and high on the W side, so that a plasma density distribution becomes non-uniform.
To solve this problem, the dipole ring magnet is rotated in its circumferential direction to change the direction of the drift motion of electrons. In practice, however, it is difficult to make the plasma density distribution uniform only by rotating the dipole ring magnet.
Further, there has been known a conventional magnetron etching apparatus including a rotary magnet as shown in FIG. 12.
This magnetron etching apparatus 120 includes a processing chamber 121, an upper electrode 122 and a lower electrode 123 provided to face each other in a vertical direction within the processing chamber 121, a magnet 124 which has a substantially circular plate shape and is provided to be rotated above or at an outside of the upper electrode 122, and a high frequency power supply 125 that applies a high frequency power to a space between the upper electrode 122 and the lower electrode 123. Further, a wafer W is provided within the processing chamber 121 (see, for example, Patent Document 2).
The magnet 124 provided above or at the outside of the upper electrode 122 generates a magnetic field B along a surface of the wafer W within the processing chamber 121. The magnet 124 is rotated at a desired rotation speed by a driving device (not illustrated) such as a motor or the like in a horizontal plane parallel to a surface of the wafer W. As a result, the magnetic field B is formed to be intersected with an electric field E applied into a space within the processing chamber 121.
In this magnetron etching apparatus 120, when a time average is taken, plasma density becomes uniform above the wafer W, but at each moment, the plasma density is still non-uniform. Further, by a drift motion of charged particles, for example, electrons, caused by a Lorentz force, the plasma density and an etching speed (etching rate) on the surface of the wafer W decreases in one direction and an electric potential (VDC) increases. That is, since the plasma density becomes non-uniform and an electric potential also becomes non-uniform, charged regions polarized positively and negatively are respectively formed at both ends of the wafer W (charge-up phenomenon).
Therefore, in order to remove the non-uniformity in plasma density distribution described in Patent Document 1 and Patent Document 2, the present applicant suggests a plasma processing apparatus that generates a magnetic field symmetric with respect to a central portion of the wafer W in a processing space. To be specific, as illustrated in FIG. 13, in a plasma processing apparatus 130, multiple permanent magnets 132 are arranged in multiple annular circles with respect to the central portion of the wafer W on an upper surface of a processing chamber 131 facing the wafer W, and a magnetic pole from each permanent magnet 132 toward the wafer W is adjusted. As a result, a magnetic field B radially distributed from the central portion of the wafer W in the processing space is generated (see, for example, Patent Document 3). Thus, electrons are rotated above the wafer W around the central portion of the wafer W by the drift motion with a Lorentz force, so that the plasma density does not simply decrease or increase in one direction and plasma is distributed symmetrically with respect to the central portion of the wafer W. As a result, non-uniformity in plasma density is removed.